This invention relates to a clamp type ammeter, and more particularly to the mechanism for opening and closing a pair of opposed magnetic cores in a center-opening clamp type ammeter.
The conventional center-opening clamp type ammeter incorporates the pair of magnetic cores adapted to open in both directions and to admit a free increase to the aperture therebetween and, therefore, enjoys an advantage that it clamps a given electric cable with great ease. Since the pair of magnetic cores are interlocked to each other so as to be synchronously opened and closed to a desired aperture, however, the mechanism serving to open and close these magnetic cores is complicated and admits little reduction in size.
For example, Japanese Patent Publication Sho. 54 (1979)-32350 discloses an invention aimed at synchronizing such a pair of magnetic cores by means of a link mechanism. This invention necessitates inclusion of a space for accommodating this link mechanism in the portion at which the magnetic cores are fastened to the ammeter proper. Japanese Utility Model Laid-open Publication Sho. 53 (1978)-56884 discloses an invention which accomplishes the synchronization of movements of a pair of magnetic cores by causing the terminal portions of a pair of magnetic cores rotatably attached through the medium of a bearing shaft to the ammeter proper to be shaped so as to rest one on top of the other, boring a slender hole through the overlapping point of the terminal portions and piercing a connecting pin through the slender hole, whereby a motion imparted to one of the two magnetic cores automatically causes the remaining magnetic core to be synchronously moved.
For center-opening clamp type ammeters of the class described above, it is important that the opening and closing operations proceed smoothly, the individual magnetic cores forming the pair should come into safe, intimate contact with each other in their completely closed state, and the mechanism used for opening and closing the magnetic cores should be simple enough to admit considerable reduction in size. For the ammeters to function perfectly on electric cables of large diameters, it is equally important that the mechanism should be provided with a special device capable of precluding the occurrence of play when the magnetic cores are in their fully opened state.